Circuit component and transformer device with controllable impedance and with systems equipped with such devices

ABSTRACT

The invention relates to a circuit component (L 1 ) with controllable impedance, comprising a body ( 1 ) of a magnetisable material, a main winding (A 1 ) wound round the body ( 1 ) about a first axis and a control winding (A 2 ) wound round the body ( 1 ) about a second axis, at right angles to the first axis, where the main winding (A 1 ) is arranged for connection to a working circuit in which the circuit component (L 1 ) is to be employed and the control winding (A 2 ) is arranged for connection to a control unit for controlling the impedance in the working circuit. The invention also relates to various current and voltage regulating devices comprising the circuit component or a similar transformer device.

The invention relates to a circuit component with a controllableimpedance of the type described in PCT/NO001/00217.

In the said patent application a circuit component is describedcomprising a body of magnetisable material, a main winding that is woundround the body about a first axis and a control winding that is woundround the body about a second axis. By altering the current in thecontrol winding it will be possible to change the circuit component'sreluctance and thereby the impedance independently of frequencyvariations in the circuit in which the main winding is connected.

The concept according to the invention therefore involves providing acircuit component with controllable impedance as indicated in patentclaim 1, where the impedance control is implemented by means of acontrol current. A major advantage of the invention is that it does notrequire movable parts or complicated circuits for controlling theimpedance value.

The principle behind the invention is illustrated in FIG. 1. In thisfigure there is illustrated a body 1 of a magnetisable material, whichmay be ferrite or iron or other suitable magnetisable materials. Aroundthe body 1 is wound a main winding A1, which will be connected to thecircuit at the point where a variable impedance requires to beintroduced. A1 is wound in a first direction, which in the caseillustrated in FIG. 1A coincides with the body's 1 circumference. Asecond winding, the control winding A2, is also wound around the body 1,but the winding axis is at right angles (perpendicular) to the windingaxis for A1, thereby largely avoiding transformative connection betweenA1 and A2, with the only connection taking place within the magnetisablematerial. In principle the connection will be manifested as a change inthe material's μ_(r). Based on the known equations: Rm=1/μ_(r)μ₀A,L=N²/Rm and X_(L)=jwL, it can be seen that a change in μ_(r) will leadto a change in L and thereby in X_(L).

This characteristic of the invention is particularly useful with regardto regulation, which at the present time is carried out by means ofpower electronics.

A first application of the circuit component according to the inventionis for series compensation in transmission lines (patent claim 2, FIG.2). Series compensation is employed in the case of a power line 12 whereconnection of various equipment causes the line's total impedance tohave an excessively high inductive factor. In order to compensate forthe inductive factor, capacitors C1 are inserted. The componentaccording to the invention L1 will then be connected in series to theline 12 where the compensation is to be performed (i.e. the main windingA1 in the component L1 is connected in series to the line 12). At thesame time the component L1 will be connected in parallel to a capacitoror a capacitor battery C1. By means of the control winding A2 in L1 itwill be possible to control the component's L1 impedance from a very lowvalue (where the current in the line 12 passes through the component L1and not through the capacitor C1) to a high value (where the current inthe line 12 largely passes through the capacitor C1). A secondapplication of series compensation is in order to change the impedancevalue for a transmission line and thereby control power flow betweenseveral parallel lines. In the case illustrated in FIG. 1 it will bepossible by means of the component L1 according to the invention tocontrol the impedance in the line 12 and thereby the load distributionbetween the lines 12 and 13. According to the prior art it is possibleby this means to perform load flow regulation (current limiting orredistribution of power flow) and stability control.

According to the prior art a series compensation of this kind is carriedout by means of a thyristor-controlled or thyristor-connected seriescapacitor (CSCS, TSSC). A thyristor group and control devices aretherefore required in order to activate the different thyristors. Thisis both cumbersome and expensive.

The invention also relates to a system for controlling the impedance ofa transmission line according to patent claims 10 and 11, and in aspecial embodiment a system for series compensation of transmissionlines according to claim 12.

Such an embodiment of the invention comprises a measuring unit 2 formeasuring parameters concerning the line's operation (U, I cos φ, P, Q,S, f), a processing unit with inputs and outputs where a first input isconnected to the measuring unit so that the results of the measurementare transmitted to the processing unit, a second input is connected toan input unit for input of desired values, and at least one output,where the output signal is converted to a current control signal with adesired frequency (this current may be direct current or alternatingcurrent) and intensity, and a circuit component with controllableimpedance comprising a main winding for connecting to the transmissionline and a control winding for connecting to the processing unit, withthe result that the processing unit controls the component's impedanceon the basis of the ratio between the measurement results and thedesired values.

It is also possible to implement the invention as an “open loop” controlcircuit where the impedance value is regulated on the basis of desiredvalues without any feedback for measurement values.

A simplified block diagram for the invention is illustrated in FIG. 3.

FIG. 3 illustrates a system according to the last-mentioned embodimentof the invention. As stated, the system comprises a measuring unit 2 forconnecting to a transmission line 12, which has to be seriescompensated, and which will measure the line's operating parameters,such as voltage, current, cos φ). The measured values are transmitted toa processing unit 4, which in an embodiment of the invention is also fedwith desired values. Based on the input values the processing unitcomputes a desired value for the impedance of the component L1 andthereby the necessary control current value that will be applied to thecontrol winding A2 in the component.

Thus the invention constitutes a controllable series reactor that may beemployed in combination with a series battery.

The invention has great utilitarian value since it will lead toincreased network utilisation (increased load limits) as a result of theability to regulate power flow (in normal operation or after a fault),or as a result of increased stability limits.

With regard to the output of the circuit component, the maximum outputmay preferably be of the order of 3000 A, with an impedance of 10-50ohm.

Regarding regulation requirements for the system, linear control of theseries inductance will be needed. The regulating system (which in thedescribed example is provided in the processing unit 4) should be ableto follow power changes with a frequency of up to 10 Hz if the unit isto be used for stability control. If it is to be used for compensationof subsynchronous resonance it will have to be raised to 30-50 Hz.

As regards protection requirements when using the system, traditionalimpedance/distance protection will be replaced by “wave protection”. Ifa series battery is used, this will result in the need for metal-oxidediverters (MOD).

As far as system losses are concerned, the stationary losses should besmall but this is a minor consideration since the component's totalutility value is high. One of the advantages of the system is that itinvolves a single component with exceptionally low operating costs.

A second application of the circuit component according to the inventionis as a shunt compensator in transmission lines (patent claim 3), i.e.as a controllable shunt reactor possibly in combination with a shuntbattery. According to the prior art this kind of shunt compensation isperformed by means of thryistor-controlled reactors (TCR), with all thedrawbacks this entails. This application of the invention is illustratedin FIG. 4.

According to this embodiment of the invention the shunt compensation isimplemented by means of a circuit component L1 with a main winding A1,which is connected on one side to a transmission line 13 and on theother side is connected to a capacitor C1. The capacitor C1 in turn isconnected to earth. The compensation is carried out by changing theimpedance of the circuit component L1 by means of the control winding A2and thereby changing the total impedance of the series L1-C1. The totalimpedance for the series connection will therefore vary from purelyinductive (high value of impedance for the component L1) to zero (seriesresonance between L1 and C1) and thereafter to purely capacitive (lowvalue of impedance for the circuit component L1). At the same time itwill be possible to perform voltage regulation by means of this device,where an unacceptably high voltage in the line will be able to becompensated by increasing the total series impedance for the componentand the capacitor and vice versa for an unacceptably low voltage.

Thus in a second embodiment, the system according to the inventioncomprises a system for shunt compensation (patent claim 13), with ameasuring unit, a processing unit and a controllable circuit componentwhere the main winding A1 is arranged for connection in parallel withthe transmission line 13, and where the system further comprises acapacitor or a capacitor battery C1 connected in series with the circuitcomponent's L1 main winding A1 for shunt compensation of thetransmission line 13.

The function of this embodiment of the invention will be reactivecompensation and voltage regulation in the transmission line.

It will lead to increased network utilisation (increased load limits) asa result of better voltage regulation (in normal operation or after afault) and reactive reserve, or also as a result of increased limitswith regard to the voltage stability.

With regard to output for the shunt reactor, this will be of the orderof 80-150 MV Ar (300 kV, 420 kV). The requirements for regulation of theprocessing unit will be similar to those for an SVC unit (band width10-20 Hz).

This system has no special protection requirements, which means thatstandard conductors (MOA) can be used.

As far as losses are concerned, these will correspond to or be lowerthan those for ordinary reactors, i.e. reactors that cannot regulate theimpedance with iron core. Control current loss will come in addition(3%). It is most relevant to compare this aspect of the invention with atraditional thyristor-controlled reactor (TCR).

A third application of the circuit component according to the inventionis for earth fault compensation (patent claim 4). The prior art in thisfield comprises the use of a so-called Petersen coil for limiting earthfault current. A Petersen coil is a reactor with an iron core and airgap, which is connected between the network's neutral point and earth.Petersen coils are extremely expensive, in addition to which they haveto be adjusted mechanically. The Petersen coil has to be regulated atall times to resonate with the rest of the system to which it isconnected. Impedance changes in the system will therefore lead to theneed for a new, mechanical adjustment of the coil. This is cumbersomeand expensive, and substantially limits the use of such a coil.

The said application of the invention is illustrated schematically inFIGS. 5 and 6. FIG. 5 illustrates a three-phase converter where theprimary windings are connected in delta configuration while thesecondary windings are connected in radial configuration. The circuitcomponent L1 according to the invention is therefore arranged betweenthe radial configuration's zero point and earth. By changing theimpedance of the circuit component L1 it will be possible to control theearth fault back or return current.

The invention also comprises a system for earth fault compensation(patent claim 14, FIG. 6), i.e. for regulating earth fault impedancecomprising a measuring unit 2 for measuring earth fault back or returncurrent together with other parameters for an electrical component T1, aprocessing unit 4 with at least one input and one output, where theinput is connected to the measuring unit 2, and in which processing unitthe measurement values are compared with desired values for earth faultback current values in order to derive an output signal constituting acontrol current signal, and a circuit component L1 with controllableimpedance with a main winding A1 for connecting between the component T1and earth and a control winding A2 for connecting to the processing unit4, with the result that the control current signal is fed to the controlwinding A2 from the processing unit 4, thereby controlling theprocessing unit 4 component's L1 impedance and earth fault current onthe basis of the ratio between the measurement results and the desiredvalues.

As regards the output of this system, this will preferably be up to 200A.

This embodiment has no special protection requirements, and the losseswill not be important since the voltage across the circuit componentwill normally be low.

A fourth application of the circuit component is as a filter (patentclaim 5), for example as shunt or series compensation with very rapidregulation.

This rapid regulation will be achieved by simply providing a rapidchange in the control current.

According to this embodiment the invention will comprise a filter (FIG.7 for band-pass filter, FIG. 8 for high-pass filter) comprising a shuntor series compensator with a main winding for connecting to the maincircuit and a control winding for connecting to a control unit. By meansof the control current, the circuit component included in the filterwill be able to change the filter's characteristics as required simplyby changing the characteristics of the control current.

A filter system according to the invention (patent claim 15) willcomprise a filter with a circuit component as mentioned earlier togetherwith a measuring and a processing unit for controlling the component'sinductance. The system's function will be compensation in order toreduce harmonic, phase asymmetry and flicker in addition to reactivecompensation.

In this application the invention will provide better voltage qualityand increased reliability in HVDC converters.

As far as the output requirement is concerned, this will vary dependingon where the filter has to be used, but in general it can be said thatas a rule it will be of the order of 50-100 MVAr. The regulation of thesystem will have to be rapid, viz. preferably from milliseconds to 1/10of a second.

The invention will therefore represent an alternative to the knownactive filters (power electronics-based), passive filters and hybridsolutions.

A fifth application of the circuit component is as a current limiter(patent claim 16), “generator switch”, such as for example a controlledseries reactor for current limiting in connection with an electricalload device. This embodiment of the invention is illustrated in FIG. 9.This embodiment is similar on the whole to that illustrated in FIG. 3,except that the control will be exclusively conducted on the basis ofdesired current values. Thus the invention will also comprise a currentlimiting system, where it will be possible to provide a switch by meansof the circuit component according to the invention. The switch willthen be able to move from an open state (i.e. very high impedance) to aclosed state (i.e. impedance equal to zero) steplessly by means of thecontrol current. By using a current limiter according to the invention,it will be possible to reduce the current supplied to the load device toa magnitude that can be handled by a circuit breaker. In this manner itwill be possible to replace power switches (which are 20 times moreexpensive than circuit breakers but which on the other hand are capableof interrupting high current values) with circuit breakers incombination with current limiters according to the invention.

In this case the function of the system will be current limiting byintroducing higher or lower impedance depending on the requirement.

With regard to the utilitarian value of this invention, the mostimportant advantage will be that it will lead to a reduction in the needfor switch equipment.

In this case the output requirement will be independent according to thepurpose for which it is used.

As regards regulation requirements, it will not be necessary to have aclosed loop for regulation.

The losses in normal “on mode” will be approximately 0 loss.

The invention will represent an alternative to an Is limiter.

We shall now present possible concrete applications of the invention.

Series Reactor Flesaker-Tegneby

With regard to possible applications in the Norwegian main network, theuse as a series reactor may be cited as an example. Limits fortransmission capacity from west to east in Southern Norway will often bedetermined by the capacity of 300 kV Flesaker-Tegneby. The reason forthis is that when central lines in Eastern Norway drop out, this willlead to an increased load on the line/cable between Flesaker andTegneby. A controllable series reactor will offer the possibility ofreducing the power flow on this connection in a fault situation, therebypermitting an increase in the operative load limits in the Flesakersection.

Traction Power Supply

Power fluctuations are an increasing problem for the traction powersupply in Norway and in other countries employing rotating converters.The converter sets in Norway consist mainly of mechanically connectedsynchronous motor-synchronous generator sets that supply the tractionpower network with single-phase alternating voltage of approximately 15kV and frequency equal to 16⅔ Hz. Stability problems associated with theconverter sets are experienced more and more frequently as a result ofthe fact that the locomotives are becoming more powerful and morerapidly regulating.

The problem is due to an inherently poor damping in the converter setsresulting in power fluctuations on the three-phase side (the networkside) and thereby a reduction in the quality of electricity. In additionthe fluctuations cause increased mechanical wear on the actual sets.

A controlled series reactor in connection with the transformer thatsupplies the converter sets from the network side may be a veryeffective measure for stabilising its operation.

Portable Control Unit for a Variety of Applications

The need for stationary control units in the network will naturally varyas a result of load changes, network development or special temporaryrequirements. It may also be envisaged that even though there willalmost always be a need for a control unit, the best position in thenetwork will change with time. It may therefore be difficult to defendsuch an investment in the network since one does not know where or forhow long there will be a need for the component.

This provides the motivation for developing compact control units, whichare transportable, and which have great flexibility with regard toapplications. By flexible applications in this context we mean bothflexibility regarding control function and connection to the network(different voltage levels, series or shunt connection, etc.).

As a specific example one may envisage a unit mounted on a semitrailerand consisting of controllable reactors, possibly in combination with acapacitor battery, and with the necessary equipment for protection andnetwork connection. The control system must be flexible andconfigurable, thus enabling the unit to be used for different purposes,such as reactive compensation, active voltage regulation and voltagequality improvement or damping of power fluctuations.

Other concrete examples of applications of the invention will be

-   -   Earth current compensation.    -   Use as a fault current limiter. Possibility of making generator        switches cheaper and smaller.

In a second embodiment the invention constitutes a circuit component inthe form of a transformer device (patent claim 7), i.e. a circuitcomponent where there are two main windings and one, or possibly twocontrol windings, thus permitting the transformer's transformation ratioto be changed by means of one or more control current(s).

Such an embodiment of the invention is illustrated in FIGS. 9 and 10.FIG. 9 illustrates two three-phase transformers comprising adjustablecircuit components. FIG. 10 illustrates the principle behind thisembodiment of the invention. Around the magnetisable body 1 is anadditional main winding A3 connected in such a manner that the windingsA1 and A3 together with the body 1 form a transformer. The controlwinding A2 is still present and will regulate the transmission ratio ofthe transformer. It is also possible to wind the main winding A3 aroundthe same axis as the control winding.

An important area of application for such a transformer will be newsystems for voltage regulation (patent claim 8) in connection withtransformers that will replace the known automatic on-load tap changers.The function will therefore be mainly voltage regulation. The advantagesof increased utilisation of transformers with a new “tap changer” are;reliability, maintenance, regulation, equally valid in all kinds ofnetwork (distribution, regional and central networks).

Amongst the advantages that will be obtained with the invention is afaster and more precise voltage regulation (simpler with coordinatedcontrol).

The output for a circuit component according to the invention will be200-2000 A.

With regard to regulation requirements, there will be no need for rapidregulation, but a regulation of the order of 10 seconds to 1 minute willsuffice.

As far as the losses are concerned, these can be compared to those forconventional transformers.

A major advantage of this embodiment of the invention is that it willlead to much lower maintenance costs compared with today's tap changers.

As alternative solutions, i.e. solutions according to the prior art, wemay mention traditional automatic tap changers.

This embodiment of the invention can also be employed in connection witha phase angle regulator (patent claim 9), which will thereby comprise atransformer component according to the invention. By regulating thecontrol current it will be possible to control the phase shift betweenthe primary and the secondary side. A phase angle regulator of this typeis illustrated in FIG. 12. In this case a variety of technical solutionscan be envisaged, such as an adjustable series transformer (aseries-connected transformer with voltage regulation). The function ofthe phase angle regulator will be mainly load flow regulation, andpossibly stabilisation.

The introduction of this embodiment of the invention will lead toincreased network utilisation (increased load limits) as a result of thepossibility for rapid regulation of load flow (in normal operation orafter a fault) and improved stability.

The power transfer will be of the order of 200-1000 MVA (132 kV-420 kV).

Regulation will depend on the function (static power distribution oralso dynamic regulation and stabilisation). For pure load flowregulation the band width requirement will be in the area of seconds(0.1-1 Hz).

The protection requirements will be the same as for the seriescompensation.

As far as losses are concerned, the stationary losses should be low, butwhat is acceptable for each application will be dependent on thecomponent's total utilisation value.

A special advantage that may be mentioned in association with thisembodiment of the invention is greater flexibility in operation of thenetwork.

The alternative solutions according to the prior art will be staticseries compensators (SSSC), phase distortion transformers, UPFC.

The voltage and phase angle regulator may advantageously form a part ofa regulation system according to the invention, where, as mentionedearlier, the system comprises a measuring unit, a processing unit andpossibly a unit for manual input of desired values.

All the above-mentioned embodiments of the invention are particularlysuitable for use on the seabed or other high-pressure locations.

1-9. (canceled)
 10. A system for controlling the impedance of atransmission line, comprising a measuring unit for measuring parametersconcerning the line's operation a processing unit with at least oneinput and one output, where the input is connected to the measuringunit, and in which processing unit the measurement values are comparedwith desired operating values for the line in order to derive an outputsignal constituting a control current signal, and a circuit componentwith controllable impedance with a main winding for connection to thetransmission line and a control winding for connection to the processingunit, with the result that the control current signal is fed to thecontrol winding from the processing unit, thereby controlling theprocessing unit component's impedance and the line's operation on thebasis of the ratio between the measurement results and the desiredvalues.
 11. A system according to claim 10, where the desired values forthe line are input manually by an operator.
 12. A system according toclaim 10, where the main winding is arranged for connection in serieswith the transmission line and the system further comprises a capacitoror a capacitor battery connected in parallel with the circuitcomponent's main winding for series compensation of the transmissionline.
 13. A system according to claim 10, where the main winding isarranged for connection in parallel with the transmission line and thesystem further comprises a capacitor or a capacitor battery connected inseries with the circuit component's main winding for shunt compensationof the transmission line.
 14. A system for earth fault compensation,i.e. for regulating earth fault impedance comprising a measuring unitfor measuring earth fault back current together with other parametersfor an electrical component, a processing unit with at least one inputand one output, where the input is connected to the measuring unit andin which processing unit the measurement values are compared withdesired values for earth fault back current values in order to derive anoutput signal constituting a control current signal, and a circuitcomponent with controllable impedance with a main winding for connectingbetween the component and earth and a control winding for connecting tothe processing unit, with the result that the control current signal isfed to the control winding from the processing unit, thereby controllingthe processing unit component's impedance and earth fault current on thebasis of the ratio between the measurement results and the desiredvalues.
 15. A filter system for reducing harmonic currents, phaseasymmetry and flicker as well as for reactive compensation of anelectrical device, where the system comprises a measuring unit formeasuring parameters-concerning the device's operation, a processingunit with at least one input and one output, where the input isconnected to the measuring unit, and in which processing unit themeasurement values are compared with desired operating values for thecomponent in order to derive an output signal constituting a controlcurrent signal, and a filter connected to the component, where thefilter comprises a circuit component with controllable impedance with amain winding for connection to the filter circuit and a control windingfor connection to the processing unit, with the result that the controlcurrent signal is fed to the control winding from the processing unit,thus controlling the processing unit component's and thereby thefilter's impedance and the device's operation on the basis of the ratiobetween the measurement results and the desired values.
 16. A switch orcurrent limiting system for an electrical device such as, e.g. anelectric motor, where the system comprises a measuring unit formeasuring parameters concerning the device's operation, a processingunit with at least one input and one output, where the input isconnected to the measuring unit, and in which processing unit themeasurement values are compared with desired operating values for thecomponent in order to derive an output signal constituting a controlcurrent signal, and a circuit component connected between the powersupply and the device, where the circuit component has a controllableimpedance with a main winding for connection between the power supplyand the device and a control winding for connection to the processingunit, with the result that the control current signal is fed to thecontrol winding from the processing unit, thereby controlling theprocessing unit component's impedance and thereby the off/on position ofthe switch substantially steplessly and thereby the device's operationon the basis of the ratio between the measurement results and thedesired values.
 17. A system according to claim 11, where the mainwinding is arranged for connection in series with the transmission lineand the system further comprises a capacitor or a capacitor batteryconnected in parallel with the circuit component's main winding forseries compensation of the transmission line
 18. A system according toclaim 11, where the main winding is arranged for connection in parallelwith the transmission line and the system further comprises a capacitoror a capacitor battery connected in series with the circuit component'smain winding for shunt compensation of the transmission line.